Iminodiacetonitrile (IDAN) is an intermediate in a route to iminodiacetic acid (IDA). IDAN can be formed by: (a) reacting ammonia, formaldehyde, and HCN; or (b) hexamethylenetetramine and HCN; or (c) glycolonitrile and ammonia in an aqueous medium. The resulting IDAN is then hydrolyzed in a hydrolysis step with an aqueous alkali metal hydroxide solution to form an alkali metal salt of iminodiacetic acid, IDA, (i.e., IDAM.sub.2 in which M is an alkali metal ion provided by the alkali metal hydroxide (e.g., IDANa.sub.2 where using sodium hydroxide as the alkali metal hydroxide)) which is acidified (generally with sulfuric acid or hydrochloric acid) in an acidification step to form IDA which will precipiatate as solid IDA. The solid IDA can be separated and recovered.
In such synthesis an effluent stream (an aqueous solution) generally containing about 0.1-10% IDAN may be encountered. The process of this invention can be used to recover IDAN values from such effluent stream to decrease the loss of a valuable intermediate and to eliminate or substantially eliminate a potential pollution source (the IDAN present in the effluent stream).
The fact that methylene chloride, an organic solvent which is substantially insoluble in water, can be used to extract IDAN from an aqueous solution containing a relatively low concentration of IDAN is surprising because U.S. Pat. No. 3,463,811, Godfrey et al, teaches that an admixture of kerosene (an organic solvent which is substantially insoluble in water) and a kerosene-soluble substantially water-insoluble amine failed to extract any appreciable amount of nitrilotriacetonitrile (NTAN) from an aqueous system comprising both dissolved and solid phase NTAN.
The respective formulas of IDAN and NTAN are: ##STR1##
Liquid-liquid extraction, which is generally called "liquid extraction" or "solvent extraction", is well known to those skilled in the art. It is taught by Perry and Chilton, "Chemical Engineers' Handbook," 5th Edition, McGraw-Hill Book Company, New York, N.Y., pages 15-2 and 15-3 (1973).